The objective of the proposed studies is to understand the mechanisms which regulate the continual exchange of cations and water between the crystalline lens and its environment. These mechanisms are essential to the cation and water balance of the lens and thus contribute to the maintenance of lens transparency. Ultimately, we hope to reach an understanding of the relationship between changes in lens cation and water balance and the development of human cataract. In the present project period, we will examine: 1) the characteristics of lens Na-K-ATPases, active cation transport and membrane permeability; 2) the role of calcium in maintaining lens membrane permeability properties; 3) the development of cataract in hypocalcemic rabbits; 4) electrical properties of lens membranes; 5) developmental aspects of lens cation balance; 6) alterations in transport and permeability during cataractogenesis in rat; 7) transport and permeability characteristics of the human lens.